US4553168A - Method and apparatus for adjusting the operating conditions of a photosensitive charge transfer device - Google Patents

Method and apparatus for adjusting the operating conditions of a photosensitive charge transfer device Download PDF

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Publication number
US4553168A
US4553168A US06/558,506 US55850683A US4553168A US 4553168 A US4553168 A US 4553168A US 55850683 A US55850683 A US 55850683A US 4553168 A US4553168 A US 4553168A
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Prior art keywords
amplitude
bias voltage
charge transfer
value
potential wells
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Expired - Fee Related
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US06/558,506
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English (en)
Inventor
Jacques Chautemps
Pierrick Descure
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/148—Charge coupled imagers
    • H01L27/14887—Blooming suppression
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
    • H04N25/745—Circuitry for generating timing or clock signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/14—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices
    • H04N3/15—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation
    • H04N3/155—Control of the image-sensor operation, e.g. image processing within the image-sensor

Definitions

  • the present invention relates to a method and to apparatus for adjusting the operating conditions of a photosensitive charge transfer device as is mainly used under very low lighting conditions.
  • the photosensitive charge transfer devices to which the present invention relates are also known as “charged coupled devices” or “CCD” and they are generally of the area type although they may in special circumstances be linear. In either case, light radiation is applied to charge transfer registers.
  • charge transfer devices are now wellknown in themselves and are described, in particular, in the work by C. H. Sequin and M. F. Thompsett entitled “Charge transfer devices", page 142 et seq.
  • the present invention is applicable to charge transfer devices which are linear charge coupled devices or surface area charge coupled devices using three or four control phases.
  • the bias voltage applied to the charge transfer registers in the image zones and in the memory zones is fixed once and for all regardless of the level of illumination received by the image zone.
  • this bias voltage determines the depth of the potential well created under said registers, in other words it determines the storage capacity of minority carriers.
  • the level of illumination is very much less than the chosen saturation level of illumination, the degree to which the potential wells are filled will be very small.
  • the depth of the potential wells has both direct and indirect effects on various features such as dark current, noise due to the control phases, etc.
  • the object of the present invention is to mitigate the above-mentioned drawbacks by providing a method of adjusting the operating conditions of a charge transfer device together with an apparatus for performing the method.
  • the dark current, and consequently the power consumption can be reduced by implementing the invention, as can the noise due to the control phases.
  • the present invention provides a method of adjusting the operating conditions of a photosensitive charge transfer device having a photosensitive zone which is constituted by charge transfer registers each having electrodes connected to a periodic bias voltage which creates potential wells having a saturation value fixed by said bias voltage, the improvement wherein the method consists in cyclically integrating the charges induced by the light image to be scanned, and, during each integration cycle, in calculating the total amplitude of the signal corresponding to said image, in comparing said calculated amplitude with a threshold amplitude value which is a function of said saturation value fixed by said bias voltage, and in modulating the amplitude of said potential wells created by said bias voltage as a function of the result of said comparison.
  • light image refers not only to visible wavelengths but also to adjacent wavelengths, and in particular to infrared wavelengths.
  • the amplitude of the potential wells may be modulated by modulating the high level or by modulating the low level of the bias voltage applied to the electrodes, i.e. the control phases of the charge transfer registers. This modulation may be obtained by successive multiplications or divisions, preferably doublings and halvings, of the bias voltage as applied to the electrodes. Naturally, the bias voltage should remain within given upper and lower limits. Since the saturation voltage of the potential wells thus created is a linear function of the bias voltage of the control phases of the charge transfer registers, the amplitude of the potential wells and thus their capacity, is decreased or increased by dividing or by multiplying said bias voltage by an integer.
  • the present invention also provides apparatus for performing the above-defined method.
  • the apparatus comprises calculator means for calculating, during each integration cycle of a light image, the amplitude of the video signal corresponding to said image, comparator means for comparing the calculated amplitude with an amplitude value which is a function of the saturation value corresponding to the bias voltage applied to the shift registers, and amplitude modulating means responsive to the result of said comparison to modulate the amplitude of the potential wells created by said bias voltage as a function of said result.
  • the amplitude modulating means is constituted by a circuit for dividing the bias voltage by two if the calculated amplitude is less than a fraction of said threshold value and providing the bias voltage is greater than its minimum value, and by a circuit for multiplying the bias voltage by two if the calculated amplitude is greater than the threshold value and providing the bias voltage is less than its maximum value.
  • FIG. 1 is a block diagram of one implementation of the invention for servo control of the amplitude of the potential wells created beneath the electrodes of the charge transfer registers;
  • FIG. 2a is a longitudinal section through a surface area photosensitive device for transferring a frame and of the type requiring four control phases;
  • FIG. 2b shows the levels of the surface potentials during charge integration in accordance with a first mode of performing the method of the present invention
  • FIG. 2c is a similar view to FIG. 2b but shows a second mode of performing the invention
  • FIG. 3 is a waveform diagram showing conventional control signals as applied to the registers in the image zone of the device shown in FIG. 2a, and
  • FIG. 4 is a waveform diagram of the control signals as applied in the case shown in FIG. 2b.
  • FIG. 1 shows one embodiment of the invention in which a servo circuit is associated with a photosensitive charge transfer device or photosensor to modulate the amplitude of the potential wells created under the electrodes which constitute the photosensitive zone of the photosensor in such a manner as to match the depth of the potential wells to the received illumination.
  • Reference 1 designates the waveform of the signal corresponding to the received light image during one integration cycle, i.e. one frame of the photosensor.
  • the signal is sent to an integrator 2 to calculate the overall voltage of the points making up the light image.
  • the signal corresponding to a frame is integrated in order to take account of the illumination over the entire light image and not just the illumination of a single point.
  • the voltage V obtained at the output from the integrator 2 is applied to a comparator 3 where it is compared with a threshold voltage which is equal, for example, to the saturation voltage which corresponds to the bias voltage applied to the electrodes of the registers in the photosensitive zone, as is explained in detail below.
  • a comparator 4 is used to compare the saturation voltage Vsat with the maximum value for saturation voltage Vsat max. If Vsat is less than Vsat max., the amplitude of the bias voltage applied to said electrodes is multiplied, e.g. by two, by means of a circuit 5. Otherwise, the said amplitude is left unchanged as represented by a line L in FIG. 1. If, on the contrary, the voltage V is less than the saturation voltage, a comparator 6 is used to compare the voltage V with a voltage equal to (Vsat)/n. If the voltage V is greater than said comparison voltage, the amplitude of the bias voltage applied to the electrodes remains unchanged as is represented by the line L'.
  • a comparator 7 is used to compare Vsat with Vsat min. If Vsat is less than Vsat min., the bias voltage applied to the electrodes remains unchanged as represented by the line L" in FIG. 1, but if Vsat is greater than Vsat min., the bias voltage applied to the electrodes is divided, e.g. by two, by means of a divider circuit 8.
  • the multiplier circuit 5 and the divider circuit 8 may both be constituted by potentiometers for adjusting the amplitude of the bias voltage applied to the electrodes or gates of the registers in the photosensitive zone, i.e. the amplitude of the control phases (9).
  • the circuit 9 for adjusting the amplitude of the control phases acts on a phase generator 10 for applying control phases to the said photosensitive device 12.
  • the amplitude of said phases is modified in accordance with the waveform diagram shown in FIG. 4 and symbolised in FIG. 1 by the reference 11.
  • Reference 13 designates a circuit for calculating Vsat from the bias voltage applied to the electrodes given that Vsat is a linear function of said bias voltage.
  • Reference 14 designates a divider circuit for generating (Vsat)/n. Arrow F indicates that the light image given by the charge transfer device is used for calculating the voltage V.
  • the device is a surface area photosensitive device of the frame transferring type and constituted in known manner from a set of vertically disposed charge transferring shift registers having an upper portion which is photosensitive and which constitutes the image zone 100 and having a lower portion which serves for temporary storage of the charges and which constitutes a memory zone 101.
  • An independently-controlled (.0.'), transfer gate 102 is located in between the image zone 100 and the memory zone 101.
  • the device 12 further includes a charge transfer shift register having parallel inputs and a serial output (not shown) said register serving to receive the charges coming from the vertical registers and to transfer them to a read stage.
  • the vertical shift registers in the image zone 100 and the memory zone 101 are formed in known manner by means of a network of adjacent MOS capacitors which are separated from one another by very small gaps.
  • the MOS capacitors may be obtained by covering P type or N type silicon substrate with a layer of silicon oxide on which the gates or electrodes are made from polycrystalline silicon.
  • other materials e.g. gallium arsenide for the substrate and a metal for the gates.
  • the photosensitive device is a device having four control phases, and consequently the electrodes of the registers are connected to respective phases .0. 1 , .0. 2 , .0. 3 , .0.
  • the present invention may be used with any kind of photosensitive device in which one-way transfer is obtained by using a suitable plurality of control phases.
  • the control phases .0. 1 , .0. 2 , .0. 3 , .0. 4 as shown in FIG. 3 are applied to the electrodes or gates in the image zone.
  • Times T and T' represent respective odd and even frames, with T 1 and T 1 ' representing the active portion of each frame and T 2 and T 2 ' representing the blanking portions thereof.
  • the charges corresponding to received light photons are integrated under the gates controlled by phases .0. 1 and .0. 2
  • time T 1 ' charges are integrated under the gates controlled by phases .0. 3 and .0. 4 .
  • the charges integrated in this manner are subsequently transferred during times T 2 and T 2 ' from the image zone 100 towards the memory zone 101 while the transfer gate 102 is at a high level.
  • the bias voltage is divided.
  • the amplitude of the control phases is divided by two and the waveform diagram shown in FIG. 4 is obtained.
  • FIG. 4 waveform diagram surface potential levels beneath the electrodes in the image zone and in the memory zone of the kind shown in FIG. 2b are obtained during the charge integration time T 1 . It can thus be seen on this figure that the potential wells created beneath the gates correspsonding to phases .0. 1 and .0.
  • FIG. 2 are of a depth which is slightly less than half the depth of the potential wells created when the normal bias voltage is applied and as shown in dashed lines in FIG. 2b.
  • the case shown corresponds to a single division of the bias voltage by two.
  • the bias voltage could be divided by two again as a function of the received illumination, and the depth of the potential wells would be reduced accordingly. This operation may be repeated or inverted as often as necessary in order to obtain potential wells having a satisfactory depth as a function of the received illumination, provided that the bias voltage remains within given limit values.
  • the above-described method it may be advantageous in the event of low light levels to increase the dynamic operation rate to the detriment of resolution by grouping together the charges corresponding to two or more points.
  • cells are reset after every two point rather than being reset after every point.
  • the signal is multiplied by two while the photon noise is multiplied by ⁇ 2, and reading noise occurs only once.
  • the signal/noise ratio is thus multiplied by at least ⁇ 2.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Solid State Image Pick-Up Elements (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)
US06/558,506 1982-12-10 1983-12-06 Method and apparatus for adjusting the operating conditions of a photosensitive charge transfer device Expired - Fee Related US4553168A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8220763 1982-12-10
FR8220763A FR2537813B1 (fr) 1982-12-10 1982-12-10 Procede de reglage des conditions de fonctionnement d'un dispositif photosensible a transfert de charge et dispositif pour sa mise en oeuvre

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GB (1) GB2131545B (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0261464A2 (fr) * 1986-09-26 1988-03-30 Siemens Aktiengesellschaft Procédé d'opération d'un analyseur d'image à semi-conducteur pour une caméra électronique à réglage automatique d'exposition
US5541645A (en) * 1994-07-28 1996-07-30 Eastman Kodak Company Method and apparatus for dynamically determining and setting charge transfer and color channel exposure times for a multiple color, CCD sensor of a film scanner

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2687265A1 (fr) * 1993-01-08 1993-08-13 Scanera Sc Dispositif de prise de vue electronique a haute dynamique et procede de prise de vue de scenes tres contrastees.
JP3571770B2 (ja) * 1994-09-16 2004-09-29 キヤノン株式会社 光電変換装置
RU2626554C1 (ru) * 2016-04-13 2017-07-28 Негосударственное (частное) образовательное учреждение высшего профессионального образования "Институт радиоэлектроники, сервиса и диагностики" Способ модуляции сигнала

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4055836A (en) * 1976-08-26 1977-10-25 Rca Corporation Charge transfer readout circuits
US4499497A (en) * 1982-12-27 1985-02-12 Rca Corporation CCD Imager with improved low light level response

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5721904B2 (fr) * 1973-10-03 1982-05-10
JPS5339211B2 (fr) * 1973-10-26 1978-10-20
US3953733A (en) * 1975-05-21 1976-04-27 Rca Corporation Method of operating imagers

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4055836A (en) * 1976-08-26 1977-10-25 Rca Corporation Charge transfer readout circuits
US4499497A (en) * 1982-12-27 1985-02-12 Rca Corporation CCD Imager with improved low light level response

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0261464A2 (fr) * 1986-09-26 1988-03-30 Siemens Aktiengesellschaft Procédé d'opération d'un analyseur d'image à semi-conducteur pour une caméra électronique à réglage automatique d'exposition
EP0261464A3 (fr) * 1986-09-26 1988-11-17 Siemens Aktiengesellschaft Procédé d'opération d'un analyseur d'image à semi-conducteur pour une caméra électronique à réglage automatique d'exposition
US5541645A (en) * 1994-07-28 1996-07-30 Eastman Kodak Company Method and apparatus for dynamically determining and setting charge transfer and color channel exposure times for a multiple color, CCD sensor of a film scanner

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FR2537813A1 (fr) 1984-06-15
GB8332479D0 (en) 1984-01-11
FR2537813B1 (fr) 1986-10-10
GB2131545A (en) 1984-06-20
GB2131545B (en) 1986-07-02

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